The objectives of the proposed research are to define the nature and hemostatic functions of the activities in plasma designated as: a) antihemophilic factor (factor VIII), and b) the factor that is deficient in von Willebrand's disease (von Willebrand's factor, von Willebrand's antigen and factor VIII related antigen). We are presently isolating both the von Willebrand's antigen and factor VIII from human and bovine plasma using conventional biochemical and immunological techniques. We propose to improve these techniques with the purpose off increasing the yields of both factors and develop modifications which will enhance the stability of the purified factor VIII. Techniques utilized by other investigators for seperating the von Willebrand's factor from factor VIII will be investigated to see if they offer any advantages over our present methods and to see if factor VIII obtained by different procedures are the same. The von Willlbrand's factor will be studied in an attempt to delineate its role in ristocetin-induced platelet aggregation and its possible role in other platelet aggregation phenomena. One aspect of the proposed study is the development of radioimmunoassays for both factor VIII and the von Willebrand's factor. The radioimmunoassays will be used to quantitate both factors in the respective deficient plasmas and will be used to identify degradation products and immunochemically active fragments formed during and following coagulation processes. Isotopic labeling of both the von Willlbrand's factor VIII will be done for several purposes. First it will be established that labeling can be accomplished and some biological activity retained. The labeled factors will then be used in studying the reactions of both factors during thrombotic events and will prove a useful handle when establishing the physical and chemical parameters of both factors.